JEE Main & Advanced JEE Main Paper (Held On 09-Jan-2019 Morning)

  • question_answer
    If a, b and c be three distinct real numbers in G.P. and \[a+b+c=xb\], then x cannot be: [JEE Main Online Paper (Held On 09-Jan-2019 Morning]

    A) -2

    B) 2

    C) -3

    D) 4

    Correct Answer: B

    Solution :

    Let 3 distinct numbers are a, ar, \[a{{r}^{2}}\] given \[a+b+c=xb\] \[a+ar+a{{r}^{2}}=xar\] \[1+r+{{r}^{2}}=xr\] \[{{r}^{2}}+r\left( 1-x \right)+1=0\] \[D\,\,>\,\,0\] \[{{(1-x)}^{2}}-4\,\,\ge \,\,0\] \[(1-x)-2)(1-x+2)\,\,\ge \,\,0\] \[\left( x\text{ }+\text{ }1 \right)\text{ }\left( x\text{ }-\text{ }3 \right)\text{ }\ge \text{ }0\] \[x\le \,-1\,\,\,\,or\,\,\,\,x\,\,\ge \,\,3\]


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